The overall objective is to understand how fibrillar and lamellar structures determine the optical properties of normal, diseased and edematous corneas and corneas that have undergone refractive surgery procedures. The Specific Aims are: 1) Determine the structural bases for diffuse clouding or haze seen in corneas that are edematous or have certain dystrophies; 2) Relate the optical properties of birefringence and small-angle polarized light scattering (SALS) in normal corneas and corneas with certain dystrophies to the underlying lamellar and fibrillar structures; and 3) Determine if light scattering from sources such as micro-striae following LASIK or haze following PRK is correlated with measurements of visual performance. Aims 1 and 2 test the model or hypothesis that measurements of light scattering or birefringence properties made on fresh tissues can provide direct indications of the presence of certain structures that are suggested by histology or by structure models. The general goal is to uncover the indicator(s) most appropriate for a given tissue. Aim 3 tests the hypothesis that objective measurements of light scattered in backward directions can be used to predict clinically significant visual impairment (e.g., reduced visual acuity and contrast sensitivity, particularly under low luminance conditions). Aims 1 and 3 have obvious clinical significance. Aim 2 has significant implications regarding the interpretation of clinical measurements of retinal nerve fiber layer thickness using scanning laser polarimetry and to the possible in vivo detection of alterations in lamellar ultrastructure that are suggested by x-ray measurements of corneas with keratoconus. For Aims 1 and 2 the approach is to use novel analytical techniques (developed by this team) which relate light scattering and birefringence properties of normal and abnormal corneas to their structures revealed by histology in conjunction with experimental measurements of the particular light scattering or birefringence properties to test these relationships in fresh tissues. For Aim 3, we will use the APL developed scatterometer to make objective measurements of corneal scattering in refractive surgery patients and in rabbits that have undergone PRK or LASIK. Measurements from patients will be correlated with clinical measurements of visual performance that are being done as part of another research project. For the rabbit study, resolution and F.A.C.T. charts will be imaged through freshly excised corneas and the potential degradation in visual performance will be correlated with scatterometer measurements.